This invention relates to a data transfer control system and, in particular, a system for controlling a data transfer using a first-in/first-out stack. The invention is also applicable to data transfer control systems utilizing other than first-in first-out stacks, for example, a last-in first-out stack (hereinafter referred to as LIFO stack).
Generally, in a data processing system such as a minicomputer, microcomputer, etc., a first-in/first-out stack, for example, (hereinafter referred to as a FIFO stack) having a data buffer function is used as an interface for data transfer.
FIG. 1 shows a conventional data transfer control system using, for example, a FIFO type stack. Reference numeral 11 is a processor and reference numeral 12 is an input/output device. Between the processor 11 and the input/output device 12 first and second FIFO stacks 13 and 14 are provided through buses. The first FIFO stack 13 is adapted to transfer data from the processor 11 to the input/output device 12 and the second FIFO stack 14 is adapted to transfer data from the input/output device to the processor 11. Usually, data are bidirectionally transferred between the processor 11 and the input/output device 12. Since, however, the conventional FIFO stack permits only a unidirectional data flow, it is necessary to provide two stacks different in direction from each other. Furthermore, data once stored in the stacks 13 and 14 can not be loaded into the processor by any access from the outside of the stack.